New Eye on Nature: The Real Constant Is Eternal Turmoil

By WILLIAM K. STEVENS

Published: July 31, 1990

IN a revision that has far-reaching implications for the way humans see the natural world and their role in it, many scientists are forsaking one of the most deeply embedded concepts of ecology: the balance of nature.

Ecologists have traditionally operated on the assumption that the normal condition of nature is a state of equilibrium, in which organisms compete and coexist in an ecological system whose workings are essentially stable. Predators and prey - moose and wolves or cheetahs and gazelles, for instance - are supposed to remain in essentially static balance. Anchovies and salmon reach a maximum population that can be sustained by their oceanic environment and remain at that level. A forest grows to a beautiful, mature climax stage that becomes its naturally permanent condition.

This concept of natural equilibrium long ruled ecological research and governed the management of such natural resources as forests and fisheries. It led to the doctrine, popular among conservationists, that nature knows best and that human intervention in it is bad by definition.

Now an accumulation of evidence has gradually led many ecologists to abandon the concept or declare it irrelevant, and others to alter it drastically. They say that nature is actually in a continuing state of disturbance and fluctuation. Change and turmoil, more than constancy and balance, is the rule. As a consequence, say many leaders in the field, textbooks will have to be rewritten and strategies of conservation and resource management rethought.

The balance-of-nature concept ''makes nice poetry, but it's not such great science,'' said Dr. Steward T. A. Pickett, a plant ecologist at the Institute of Ecosystem Studies of the New York Botanical Garden at Millbrook, N.Y. He was a co-organizer of a symposium that explored the matter yesterday in Snowbird, Utah, at the annual meeting of the Ecological Society of America, the nation's premier organization of ecological scientists.

While the shift in thinking has not yet produced a coherent new theory to replace the old one, Dr. Pickett characterizes what is going on as ''a major revision of one of our basic assumptions of how the natural world works.'' The developing conviction that nature is ruled more by flux and disturbance is ''becoming the dominant idea,'' he said.

''There will always be people who will cling to old ideas,'' said Dr. Simon A. Levin, a Cornell University ecologist who is the incoming president of the Ecological Society. ''But certainly the center of mass of thinking'' among ecologists, he said, has shifted away from equilibrium and toward the fluctuating nature of natural systems.

Some scientists now say that ecological communities of plants and animals are inherently unstable, largely because of idiosyncratic differences in behavior among communities and individuals in them. A super-aggressive wolfpack leader, for example, can greatly increase the pack's hunting efficiency and destabilize the ecosystem - just as the death of a pack leader can promote instability.

But even if ecological communities do display some sort of internal equilibrium, many scientists believe, external disturbances like climatic change, year-to-year variations in weather patterns, fires, windstorms, hurricanes and disease seldom, if ever, give the communities a chance to settle into a stable state. In this view, the climax forest, the neatly symmetrical predator-prey relationship and the bumper fish population become transient conditions at best, even in the absence of human intervention.

Scientists are finding this to be true on many scales of time and space, from the glacial and global to the seasonal and local, and in parts of the world long considered the most pristine and stable like the tropical rain forests of South and Central America, for instance, or the north woods of Canada and the northern United States.

In the natural landscape, ''there is almost no circumstance one can find where something isn't changing the system,'' said Dr. George L. Jacobson Jr., who, as a paleoecologist at the University of Maine, studies ecological change as it is revealed in ancient sediments and rocks. And while there may be a tendency toward a stable equilibrium, he said, ''it's never allowed to get there, so we might as well not expect it to exist.''

A Difficulty

Posing a Question: What Is Natural?

In this developing new perspective, humans are emerging as just one of many sources of ecological disturbance that keep nature in a perpetual state of uproar. The question of whether humans should intervene in natural processes is moot, ecologists say, since humans and their near-human ancestors have been doing so for eons, and ecological systems around the world bear their indelible imprint.

The supposedly pristine rain forests of Latin America, for instance, owe some of their character to the intervention of humans who planted and transplanted trees and other plants throughout the jungle. And the supposedly unspoiled Serengeti plain of Africa, some ecologists are convinced, owes its tremendous abundance of grazing animals at least partly to human-set fires that created savanna habitats.

The real question, ecologists say, is which sort of human interventions should be promoted and which opposed.